The present invention relates generally to the art of welding power supplies. More specifically, it relates to engine driven welding power supplies that include a dig and/or a hot start output.
Engine driven welding power supplies may be powered by a DC generator or an AC generator (also called an alternator-rectifier). An AC generator generally includes, in addition to an alternator, a reactor followed by rectifiers to provide a DC output. AC driven welding power supplies are, generally, constant current type machines and the output volt-ampere characteristic of an AC driven welding power supply typically has a negative, slope (decreasing voltage results in increasing current). That is, the output current is nearly constant over a varying range of output voltage. Such welding power supplies are particularly well suited for welding applications requiring an approximately constant current output (such as flat plate welding). Output current changes over a wide range are often provided by selecting a tap on the reactor. One such prior art engine-driven welding power supply is the Miller Big Blue 302(copyright) welding power supply.
An engine driven welding power supply, as used herein, is a welding power supply that may be powered by a generator. It can include (but is not limited to) the engine and the generator. A welding V-A curve, as used herein, is the graph formed when output voltage is plotted against output current. Generally, the current is on the horizontal axis and the voltage on the vertical axis. The output V-A curve slope is the slope of the graph, and a less steep slope means that a decrease in arc voltage results in a greater increase in output current. Welding range, as used herein, refers to the portion of the output curve at which welding is typically performed, such as from about 20 volts to about 40-50 volts. The V-A curve over the welding range for a constant current machine typically has an almost vertical slope. Below a welding range, as used herein, refers to an output voltage less than that at which welding is typically performed (less than about 20 volts in some systems). A dig output, as used herein, refers to the output below a typical welding range where current increases as arc length (and hence arc voltage) decreases. A hot start output, as used herein, also refers to the output below a typical welding range, and allows the welding process to be initiated with a greater current than the current that will be provided after the process has reached its operating point. The hot start current is often provided at a reduced output voltage, below the welding range, where the V-A curve has less steep slope. The range at which a dig output or a hot start output is provided is below the welding range, even though welding may be performed by the dig and/or hot start output.
A dig output is desirable to provide the user with control of the heat into the weld puddle. With a dig output, shortening the arc length reduces output voltage, which increases output current, and thus increases heat unto the weld puddle. Likewise, a hot start is desirable because it allows the welding process to be started with additional heat.
DC welding generators have a V-A output curve such that as output voltage decreases, output current increases, i.e., suitable DC machines provide a xe2x80x9cdroopxe2x80x9d or a natural dig in the V-A curve. Thus, a welder using a DC driven welding power supply can control the temperature of the welding puddle by varying the distance of the electrode from the workpiece. When the electrode is pulled back, the arc (output) voltage increases while the output current decreases. When the electrode is in close proximity to the workpiece, the arc voltage decreases (short circuit condition) while the output current increases.
AC generators do not have the natural dig output. One prior art engine-driven welding power supply system described in U.S. Pat. No. 5,734,147, issued Mar. 31, 1998, entitled Method And Apparatus For Electronically Controlling The Output Of A Generator Driven Welding Power Supply, hereby incorporated by reference, provides a dig and hot start output by electronic field control shaping of the V-A curve. Electronic field control allows the output V-A curve to be shaped as desired, including providing a dig output and hot start output below the welding range. However, such an engine-driven welding power supply is relatively complex, has a response slowed by the inductance of the field windings, and while suitable for some welding applications such as pipe welding, provides more versatility (and expense) than needed for other welding applications.
Other systems that provide a dig output use an inverter or converter based power supply, such as the power supply disclosed in U.S. Pat. No. 6,107,602, entitled Switchable power supply with electronically controlled output curve and adaptive hot start, issued Aug. 22, 2000 to Geissler, et. al. Such power supplies can provide a dig output by controlling the converter/inverter output. However, converter/inverter power supplies tend to be more complex, and suitable for particular applications.
AC systems that do not have electronic field control for output curve shaping, such as the Miller Big Blue 302(copyright), do not have a ready means of providing a dig output and a hot start output. The V-A curve does not provide a substantially vertical slope over the welding range and a less steep slope below the welding range for the dig output. Accordingly, an engine-driven welding power supply system that provides for a dig output and/or a hot start output created other than by field control is desirable. Preferably, such a system will be economical, and will be readily provided without complex circuitry.
According to a first aspect of the invention an engine driven welding power supply includes a welding output winding, and a second output winding. The welding output winding has a welding output with a welding V-A curve of a first slope, both in a welding range and below the welding range. The second output winding has a second output with a second V-A curve of a second slope below the welding range. The second slope is less steep than the first slope. An output circuit is connected to receive and combine the welding and second outputs to provide a power supply output.
According to a second aspect of the invention an engine driven welding power supply includes a welding output winding with a welding output, and a second output winding with a second output. An output circuit receives and combines the welding and second outputs to provide a power supply output with a breakpoint at a threshold at the bottom of a welding range.
A resistor is between the second output winding and the output circuit, or the coupling of the second output winding is less than the coupling of the welding output winding in various embodiments.
The welding and second output windings are part of separate generators, or part of the same generator, in other embodiments.
A rectifier circuit is disposed between the second output winding and the output circuit, and/or the combination of the second output winding and the rectifier circuit is in parallel with the welding output winding in various embodiments.
The second winding is a dig winding and the second output is a dig output, and/or the second winding is a hot start winding and the second output is a hot start output in other alternatives.
According to a third aspect of the invention a method of providing welding power output includes generating welding power from a welding winding. The welding power has a V-A curve with a first slope in and below a welding range. Additional power is generated from a second winding. The additional power has a V-A curve with a second slope below the welding range, and the second slope is less steep than the first slope. The welding power and additional power are added to provide the welding power output.
According to a fourth aspect of the invention a method of providing welding power output includes generating welding power, generating additional power, and adding the additional power and the welding power to provide a welding output having a breakpoint at a threshold at the bottom of a welding range.
The additional power is provided through an impedance, and/or generating additional power includes generating impedance-limited power in alternatives.
Generating welding power includes turning one or two generators in other alternatives.
The additional power is rectified, is dig power, and/or is hot start power in various alternatives.
Other principal features and advantages of the invention will become apparent to those skilled in the art upon review of the following drawings, the detailed description and the appended claims.